diff --git a/clean_files.txt b/clean_files.txt
index 54180c19..016915ac 100644
--- a/clean_files.txt
+++ b/clean_files.txt
@@ -76,6 +76,7 @@ completion/available/vuejs.completion.bash
 completion/available/wpscan.completion.bash
 
 # libraries
+lib/appearance.bash
 lib/colors.bash
 lib/helpers.bash
 lib/history.bash
diff --git a/lib/appearance.bash b/lib/appearance.bash
index 6d0ef2ff..9f02f74f 100644
--- a/lib/appearance.bash
+++ b/lib/appearance.bash
@@ -1,19 +1,18 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 
 # colored ls
 export LSCOLORS='Gxfxcxdxdxegedabagacad'
 
-if [[ -z "$CUSTOM_THEME_DIR" ]]; then
-    CUSTOM_THEME_DIR="${BASH_IT_CUSTOM:=${BASH_IT}/custom}/themes"
-fi
+: "${CUSTOM_THEME_DIR:="${BASH_IT_CUSTOM:=${BASH_IT}/custom}/themes"}"
 
 # Load the theme
-if [[ $BASH_IT_THEME ]]; then
-    if [[ -f $BASH_IT_THEME ]]; then
-        source $BASH_IT_THEME
-    elif [[ -f "$CUSTOM_THEME_DIR/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash" ]]; then
-        source "$CUSTOM_THEME_DIR/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash"
-    else
-        source "$BASH_IT/themes/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash"
-    fi
+# shellcheck disable=SC1090
+if [[ -n "${BASH_IT_THEME:-}" ]]; then
+	if [[ -f "${BASH_IT_THEME}" ]]; then
+		source "${BASH_IT_THEME}"
+	elif [[ -f "$CUSTOM_THEME_DIR/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash" ]]; then
+		source "$CUSTOM_THEME_DIR/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash"
+	else
+		source "$BASH_IT/themes/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash"
+	fi
 fi