style.css

/* Reset Browser Default CSS */
* {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
}
li {
	list-style: none;
}
input,
textarea {
	border: none;
	outline: none;
	font-size: 16px;
	resize: none;
}
body,
textarea {
	font-family: sans-serif;
}

/* Custom Properties */
:root {
	--theme-border: 1px solid #ddd;
	--primary-color: hsl(207, 90%, 54%);
}

#header {
	width: 100%;
	height: 60px;
	display: flex;
	align-items: center;
	justify-content: center;
	text-align: center;
	border-bottom: var(--theme-border);
}

.task-form {
	margin: 20px auto;
	padding: 10px;
	max-width: 400px;
	width: 95%;
	height: 160px;
	border: var(--theme-border);
	border-radius: 10px;
}

#task-input {
	padding: 4px;
	display: block;
	width: 100%;
	height: calc(100% - 35px);
	background-color: hsl(207, 30%, 90%);
	border-radius: 4px;
}

#task-input:focus {
	background: none;
	border: 1px solid var(--primary-color);
}

#task-add {
	margin-top: 5px;
	display: block;
	width: 100%;
	height: 30px;
	background-color: var(--primary-color);
	color: #fff;
	border-radius: 4px;
	cursor: pointer;
}

#task-add:active {
	background-color: hsl(207, 90%, 48%);
}

.tasks-wrapper {
	margin: auto;
	padding: 12px;
	width: 80%;
	border: var(--theme-border);
	border-radius: 10px;
}

.tasks-wrapper h2 {
	margin-bottom: 10px;
	font-size: 1.4rem;
	font-weight: normal;
	border-bottom: 1px solid #000;
}

.task {
	margin-top: 6px;
	padding: 4px;
	width: 100%;
	min-height: 26px;
	background-color: hsl(207, 10%, 95%);
}

@media screen and (max-width: 500px) {
	.tasks-wrapper {
		width: 95%;
	}
}