Почему бы просто не поставить цвет фона на родительском?
/* Box sizing rules */
*,
*::before,
*::after {
-webkit-box-sizing: border-box;
box-sizing: border-box;
}
/* Remove default padding */
ul[class],
ol[class] {
padding: 0;
}
/* Remove default margin */
body,
h1,
h2,
h3,
h4,
p,
ul[class],
ol[class],
li,
figure,
figcaption,
blockquote,
dl,
dd {
margin: 0;
}
/* Set core body defaults */
body {
min-height: 100vh;
scroll-behavior: smooth;
text-rendering: optimizeSpeed;
line-height: 1.5;
font-family: Arial, Helvetica, sans-serif;
}
/* Remove list styles on ul, ol elements with a class attribute */
ul[class],
ol[class] {
list-style: none;
}
/* A elements that don't have a class get default styles */
a:not([class]) {
text-decoration-skip-ink: auto;
}
/* Make images easier to work with */
img {
max-width: 100%;
display: block;
}
/* Natural flow and rhythm in articles by default */
article > * + * {
margin-top: 1em;
}
/* Inherit fonts for inputs and buttons */
input,
button,
textarea,
select {
font: inherit;
}
/* Remove all animations and transitions for people that prefer not to see them */
@media (prefers-reduced-motion: reduce) {
* {
-webkit-animation-duration: 0.01ms !important;
animation-duration: 0.01ms !important;
-webkit-animation-iteration-count: 1 !important;
animation-iteration-count: 1 !important;
-webkit-transition-duration: 0.01ms !important;
transition-duration: 0.01ms !important;
scroll-behavior: auto !important;
}
}
/*````````````````the actual code below`````````````*/
.nav {
display: -webkit-box;
display: -ms-flexbox;
display: flex;
-ms-flex-wrap: nowrap;
flex-wrap: nowrap;
height: 100px;
background-color: #ecdfc8;
}
.nav__img {
-webkit-box-flex: 1;
-ms-flex: 1 1 10%;
flex: 1 1 10%;
}
.nav img {
height: 100px;
margin: auto;
}
.nav__section {
-webkit-box-flex: 8;
-ms-flex: 8 1 90%;
flex: 8 1 90%;
display: -webkit-box;
display: -ms-flexbox;
display: flex;
-webkit-box-pack: justify;
-ms-flex-pack: justify;
justify-content: space-between;
}
.nav__ul {
display: -webkit-box;
display: -ms-flexbox;
display: flex;
-ms-flex-pack: distribute;
justify-content: space-around;
-webkit-box-align: center;
-ms-flex-align: center;
align-items: center;
}
.nav__ul--lf {
width: 50%;
}
.nav__ul--rt {
width: 15%;
}
.nav__item {
display: -webkit-box;
display: -ms-flexbox;
display: flex;
background-color: #df7861;
border-radius: 5px;
-webkit-transition: background-color 1s;
transition: background-color 1s;
padding: 10px 15px;
}
.nav a {
color: #111;
text-decoration: none;
font-weight: 300;
}
.nav__item:hover {
background-color: #df7861;
background-color: #ecdfc8;
}
/*# sourceMappingURL=style.css.map */
<header class="header">
<nav class="header__nav nav">
<span class="nav__img b1">
<img src="./img/plant-logo.png" alt="logo">
</span>
<section class="nav__section nav_section--1 b2">
<ul class="nav__ul nav__ul--lf b3">
<li class="nav__item">
<a href="www.google.com">Home</a>
</li>
<li class="nav__item">
<a href="www.google.com">Product</a>
</li>
<li class="nav__item">
<a href="www.google.com">Learn</a>
</li>
</ul>
<ul class="nav__ul nav__ul--rt b4">
<li class="nav__item">
<a href="www.google.com">Contact</a>
</li>
<li class="nav__item">
<a href="www.google.com"><span>Sign in</span></a>
</li>
</ul>
</section>
</nav>
</header>