Почему иногда происходит разрыв между divами, когда я изменяю размер моего браузера?

Question

Если вы измените размер браузера, между нижней частью .services-items и родительским div (.services) будет пробел. Вот код:

#one {
  background-color: #fff;
  height: 50%;
  width: 100%;
}
#two {
  background-color: #fff;
  height: 50%;
  width: 100%;
}
body,
html {
  height: 100%;
  background-color: #000;
}
* {
  margin: 0;
}
.services {
  background: green;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: horizontal;
  -webkit-box-direction: normal;
  -ms-flex-direction: row;
  flex-direction: row;
  padding: 0 50px;
  color: #fff;
}

.services-items {
  -webkit-box-flex: 1;
  -ms-flex-positive: 1;
  flex-grow: 1;
  background-color: rgba(0, 0, 0, 0.5);
  padding: 50px;
  height: auto;
  text-align: center;
  position: relative;
}
.services-items h2 {
  margin: 20px 0;
}
.services-items p {
  line-height: 150%;
}

<div id="one"></div>


<div class="services">
  <a>
    <div class="services-items">
      <h2>Service 1</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Similique amet atque recusandae, consequatur facere nesciunt. Placeat nostrum, aliquam suscipit. Tempore obcaecati sed eligendi cumque! Quo et, quod veniam nulla maxime quos voluptas harum
        odio ipsam libero repellat dicta hic. Eos!</p>

    </div>
  </a>
  <a>
    <div class="services-items">
      <h2>Service 2</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Perferendis pariatur vitae illum, alias suscipit ipsa soluta optio eos officia ducimus incidunt maiores molestias velit, delectus libero, ad eaque repellendus. Rerum, rem doloribus, cupiditate
        quos ex hic porro distinctio beatae. Vero, harum, autem. Quo itaque assumenda, mollitia et repellendus vel porro.</p>

    </div>
  </a>
  <a>
    <div class="services-items">
      <h2>Service 3</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Praesentium error et animi, porro omnis facilis voluptatum vel voluptatem pariatur quasi debitis in ratione voluptas eos ex maiores adipisci, nesciunt aliquid alias maxime accusamus veritatis?
        Dignissimos, perspiciatis deserunt numquam animi rerum aliquid mollitia, blanditiis dolore architecto.</p>
      <h3>Jos haluat tämän palvelun/tuotteen, ota yhteyttä ja kerro viestissä.</h3>
    </div>
  </a>
</div>


<div id="two"></div>

Answer 1

Еще одно решение для вашего кода

.services a {
   display: flex;
   align-self: stretch; 
}

Answer 2

Добавьте height:100% к service-items, а также добавьте

*{box-sizing:border-box;} к вашему CSS-файлу

Это необходимо, потому что border-box

Включает отступы и рамкув общей ширине и высоте элемента:

*{box-sizing:border-box;}

#one {
  background-color: #fff;
  height: 50%;
  width: 100%;
}
#two {
  background-color: #fff;
  height: 50%;
  width: 100%;
}
body,
html {
  height: 100%;
  background-color: #000;
}
* {
  margin: 0;
}
.services {
  background: green;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: horizontal;
  -webkit-box-direction: normal;
  -ms-flex-direction: row;
  flex-direction: row;
  padding: 0 50px;
  color: #fff;
}

.services-items {
  -webkit-box-flex: 1;
  -ms-flex-positive: 1;
  flex-grow: 1;
  background-color: rgba(0, 0, 0, 0.5);
  padding: 50px;
  height: 100%;
  text-align: center;
  position: relative;
}
.services-items h2 {
  margin: 20px 0;
}
.services-items p {
  line-height: 150%;
}

<div id="one"></div>


<div class="services">
  <a>
    <div class="services-items">
      <h2>Service 1</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Similique amet atque recusandae, consequatur facere nesciunt. Placeat nostrum, aliquam suscipit. Tempore obcaecati sed eligendi cumque! Quo et, quod veniam nulla maxime quos voluptas harum
        odio ipsam libero repellat dicta hic. Eos!</p>

    </div>
  </a>
  <a>
    <div class="services-items">
      <h2>Service 2</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Perferendis pariatur vitae illum, alias suscipit ipsa soluta optio eos officia ducimus incidunt maiores molestias velit, delectus libero, ad eaque repellendus. Rerum, rem doloribus, cupiditate
        quos ex hic porro distinctio beatae. Vero, harum, autem. Quo itaque assumenda, mollitia et repellendus vel porro.</p>

    </div>
  </a>
  <a>
    <div class="services-items">
      <h2>Service 3</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Praesentium error et animi, porro omnis facilis voluptatum vel voluptatem pariatur quasi debitis in ratione voluptas eos ex maiores adipisci, nesciunt aliquid alias maxime accusamus veritatis?
        Dignissimos, perspiciatis deserunt numquam animi rerum aliquid mollitia, blanditiis dolore architecto.</p>
      <h3>Jos haluat tämän palvelun/tuotteen, ota yhteyttä ja kerro viestissä.</h3>
    </div>
  </a>
</div>


<div id="two"></div>